A water-cooling type cooling structure configured to cool an engine and the like of a straddle-type vehicle such as a motorcycle includes a water pump configured to discharge cooling water, a water jacket configured to cool the engine by the cooling water discharged from the water pump, a radiator configured to cool the cooling water after cooling the engine, and a thermostat configured to control a flow rate of the cooling water to circulate in the radiator, based on a temperature of the cooling water.
The water jacket is provided in the vicinity of a part of the engine, from which high heat is to be generated, such as a peripheral wall of a cylinder and an inside of a cylinder head. The water pump is generally mounted to the engine. The radiator is mounted to a place of the straddle-type vehicle such as a front of the engine, which is likely to collide with wind upon traveling.
Also, the water-cooling type cooling structure has a radiator inflow path through which the cooling water discharged from the water pump and circulated in the water jacket is to flow into the radiator, a radiator outflow path through which the cooling water caused to flow out from the radiator is to return to the water pump, and a radiator bypass path branched on the way of the radiator inflow path and joining on the way of the radiator outflow path. The radiator bypass path is a path for returning the cooling water having circulated in the water jacket to the water pump without circulating the cooling water in the radiator. The thermostat is arranged at a position at which the radiator bypass path and the radiator outflow path join, for example, and is configured to control a ratio of a flow rate of the cooling water to circulate in the radiator and a flow rate of the cooling water to circulate in the radiator bypass path.
Patent Document 1 discloses a motorcycle having a water-cooling type cooling structure.
Patent Document 1: JP-A-2015-81575
In order to improve a design property of an outer appearance of the straddle-type vehicle, it is preferable that the cooling structure is made to be inconspicuous, when seeing the straddle-type vehicle from an outside. Also, it is preferably to reduce a width of an engine unit including the engine and components mounted to the engine such as a drive system, an intake system, an exhaust system and the like.
Regarding this, according to the motorcycle disclosed in Patent Document 1, the water pump, a cooling water piping configured to interconnect a cylinder block and an inlet of the radiator, and a cooling water piping configured to interconnect an outlet of the radiator and the water pump are arranged above the engine. Also, Patent Document 1 does not disclose arrangement of the thermostat. However, since the cooling water piping configured to interconnect the cylinder block and the inlet of the radiator and the cooling water piping configured to interconnect the outlet of the radiator and the water pump are arranged above the engine, it is thought that it is not difficult to arrange the thermostat above the engine. Like this, since the components configuring the cooling structure are arranged above the engine, it is thought that it is possible to cover and hide the components with a fuel tank and to thus make the components inconspicuous. Also, since the components configuring the cooling structure are arranged above the engine, it is thought that it is easy to reduce the width of the engine unit.
However, according to the motorcycle disclosed in Patent Document 1, it is necessary to secure a space for arranging the components configuring the cooling structure above the engine. For this reason, it is difficult to arrange a large fuel tank above the engine, so that it is difficult to increase a capacity of the fuel tank.